Make enum values typed strings (#18)

This also moves validation into the parsing process and refactors a bunch of code related to the config.

Reviewed-on: #18
Co-authored-by: Anna Rose Wiggins <annabunches@gmail.com>
Co-committed-by: Anna Rose Wiggins <annabunches@gmail.com>

internal/configparser/ruletype.go

@@ -0,0 +1,53 @@
+package configparser
+
+import (
+	"fmt"
+	"strings"
+)
+
+// TODO: maybe these want to live somewhere other than configparser?
+type RuleType string
+
+const (
+	RuleTypeNone          RuleType = ""
+	RuleTypeButton        RuleType = "button"
+	RuleTypeButtonCombo   RuleType = "button-combo"
+	RuleTypeButtonLatched RuleType = "button-latched"
+	RuleTypeAxis          RuleType = "axis"
+	RuleTypeAxisCombined  RuleType = "axis-combined"
+	RuleTypeAxisToButton  RuleType = "axis-to-button"
+	RuleTypeAxisToRelaxis RuleType = "axis-to-relaxis"
+	RuleTypeModeSelect    RuleType = "mode-select"
+)
+
+var (
+	ruleTypeMap = map[string]RuleType{
+		"button":          RuleTypeButton,
+		"button-combo":    RuleTypeButtonCombo,
+		"button-latched":  RuleTypeButtonLatched,
+		"axis":            RuleTypeAxis,
+		"axis-combined":   RuleTypeAxisCombined,
+		"axis-to-button":  RuleTypeAxisToButton,
+		"axis-to-relaxis": RuleTypeAxisToRelaxis,
+		"mode-select":     RuleTypeModeSelect,
+	}
+)
+
+func ParseRuleType(in string) (RuleType, error) {
+	ruleType, ok := ruleTypeMap[strings.ToLower(in)]
+	if !ok {
+		return RuleTypeNone, fmt.Errorf("invalid rule type '%s'", in)
+	}
+	return ruleType, nil
+}
+
+func (rt *RuleType) UnmarshalYAML(unmarshal func(data interface{}) error) error {
+	var raw string
+	err := unmarshal(&raw)
+	if err != nil {
+		return err
+	}
+
+	*rt, err = ParseRuleType(raw)
+	return err
+}